Brush gear in small electric motors, in particular fractional horsepower permanent magnet direct current (PMDC) motors, typically comprises a carbon brush which is carried on an end of a resilient, electrically conducting arm--the brushleaf. The brushleaf is arranged to bias the brush against a commutator on the motor shaft. Typically the brush gear is mounted in an end cap which carries a bearing for the motor shaft and forms a structural part of the motor assembly.
As a brush wears down the supporting brushleaf moves closer to the commutator. There is a danger that the brushleaf may snag on the commutator, in particular that it may catch in between segments of the commutator, and be dragged around with the rotating commutator. This may result in the brush or brushleaf making electrical contact with the other brush or brushleaf, directly or via a common commutator segment. This shorting between the brushleaves can be very dangerous, leading to the risk of fire in some PMDC motor applications.